[SIPForum-discussion] G 723 Audio Codec Bit Rate

sreekant nair sreekant_nair at yahoo.com
Fri Jul 27 16:16:57 UTC 2007

Thanks Boris, 

However, the situation is a little bit more tricky. 

It was my understanding that codec negotiation is done using the SDP. I tried capturing the INVITE - 18X - 2XX msg using Ethereal to see if there is anything that specifies the bit rate that will be used. In all cases, the codec alone is specified. Even though G.723 supports dual bit rates, I could not find anything which explicitly states the bit rate. (At least Ethereal does not decode it so). Is there something I am missing here. 

During a test scenario, both nodes negotiated and agreed on G.723 but one node sent using 5.3kbps while the other replied with 6.3Kbps and the audio path was established. This was found by the amount of data bytes in the RTP packets - one way it was 20 while it was 24 in the reverse direction. 
My question was - Is it possible (both from a hardware/software perspective) to change the bit rates while an RTP session is in progress. So to change the bit rates, there is no need of codec re-negotiation and no UPDATE / RE-INVITE would be sent. Hence my confusion and requirement. 

Not sure if I made myself clear. 


----- Original Message ----
From: Boris vercher <boris.vercher at ilexia.com>
To: sreekant nair <sreekant_nair at yahoo.com>; discussion at sipforum.org
Sent: Friday, July 27, 2007 10:00:56 AM
Subject: RE: [SIPForum-discussion] G 723 Audio Codec Bit Rate


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No it’s not
possible , if there are no codec renegotiation


There are no
compatibility between this two compressions


Vercher Boris


De :
discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] De la part de sreekant nair

Envoyé : vendredi 27
juillet 2007 15:17

À :
discussion at sipforum.org

Objet : [SIPForum-discussion]
G 723 Audio Codec Bit Rate


Hi All, 


In our system being tested, one of the codecs used is G.723
audio codec

G.723 has two bit rates - 5.3Kbps & 6.3 Kbps. 


Is is possible that during a voice call, the codec can
dynamically change the bit rate between 5.3Kbps or 6.3 Kbps ?


Any thoughts are greatly appreciated. 



Sreekant Nair



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